Windshield wiper drive linkage arm with interior grooves

ABSTRACT

This invention relates to windshield wiper system and method which utilizes a flexible member to account for compression loads in excess of a predetermined load, such as 30 percent, greater than a maximum load for the flexible member. The system utilizes a flexible pultruded composite material having a relatively low modulus of elasticity, yet relatively high elongation characteristics. The flexible arm bends to facilitate preventing damage to components in the wiper system when a compressive load applied to the flexible member is in excess of the predetermined load.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a windshield wiper system and, moreparticularly, to a windshield wiper system which utilizes at least oneflexible member which bends or flexes to compensate for compressionloads in excess of a predetermined load.

[0003] 2. Description of the Related Art

[0004] In the field of windshield wiper systems, wiper arms having wiperblades thereon are driven from a park position, where the blades areoften situated at either the bottom of or below a windshield of avehicle, through an inwipe position, to an outwipe position. Duringnormal wiping operations, the blades oscillate between the inwipe andoutwipe positions to clean the windshield of debris or particles, suchas ice, snow or other debris. It is not uncommon that snow or ice canaccumulate on the windshield and prevent the wiper blades from, forexample, fully retracting from the inwipe position to the park positionwhen a user actuates a wiper switch to an off position.

[0005] When the debris blocks the wiper arms and blades, a considerableamount of stress is imparted on the wiper linkage and drive motor whichdrives the blades. For example, a motor drive link, which couples thedrive shaft of the motor to the drive linkage which drives the wiperarms, often experiences a compressive force. The linkage members of thewiper systems have in the past been stiffened to reduce expansion andshrinkage in order to avoid changing the wipe pattern requirements forthe vehicles. However, in freezing, snowy weather, the snow and icepacks at the bottom of the windshield causes a restriction in themovement in the wiper arm and blade. Because of the rigidity of themotor drive link, the housing which houses the drive gears of the drivemotor may crack or break. It has also been experienced that one or moredrive plates which directly or indirectly couple the drive link to otherlinkage have been known to fracture or crack.

[0006] U.S. Pat. Nos. 6,148,470 and 6,381,800 illustrate a compositearm, which are incorporated herein by reference and made a part hereof.Benefits of those inventions are taught in the article “A Novel Use of aComposite Material to Limit the Loads in Windshield Wiper Systems”,Penrod, et al., Copyright 2001 Society of Automotive Engineers, Inc.,which is incorporated herein by reference and made a part hereof.

[0007] Accordingly, what is needed is a simple, yet effective, linkagesystem which utilizes one or more linkage arms having a relatively lowmodulus of elasticity with relatively high elongation and fatigueproperties to facilitate avoiding the problems of the past.

SUMMARY OF THE INVENTION

[0008] In one aspect this invention comprises a windshield wiper drivelinkage for use in a wiper system comprising a plurality of linkagearms, at least one of the plurality of linkage arms comprising acomposite flexible arm which bends to facilitate preventing damage tocomponents in the wiper system when a compressive load applied to atleast one of the plurality of linkage arms exceeds a predetermined loadas a result of a fatigue condition, at least one of the plurality oflinkage arms comprise an interior groove on each side of an end of thearm to facilitate providing an interlocking joint when a connector isovermolded onto each end.

[0009] In another aspect this invention comprises a first wiper, asecond wiper, a windshield wiper drive linkage coupled to the first andsecond wipers, a drive motor coupled to the windshield wiper drivelinkage, and the windshield wiper drive linkage comprising a pluralityof linkage arms coupled to the first and second wipers and the drivemotor, at least one of the plurality of linkage arms comprising acomposite flexible arm which bends to facilitate preventing damage tocomponents in the wiper system when a compressive load applied to atleast one of the plurality of linkage arms exceeds a predetermined loadas a result of a fatigue condition, at least one of the plurality oflinkage arms comprising an interior groove on each side of an end of thearm to facilitate providing an interlocking joint when a connector isovermolded onto each end.

[0010] Other objects and advantages of the invention will be apparentfrom the following description, the accompanying drawings, and theappended claims.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

[0011]FIG. 1 is a general schematic view of a wiper blade drive andlinking system in accordance with one embodiment of the invention;

[0012] FIGS. 2A-2D are illustrations of the wiper blade assembly of FIG.1 as it is driven from an outwipe position towards inwipe and parkpositions;

[0013]FIG. 3 is a perspective view of a flexible member in accordancewith one embodiment of the invention;

[0014]FIG. 4 is a front view of the flexible member shown in FIG. 3;

[0015]FIG. 5 is a plan view of the flexible member shown in FIG. 3;

[0016]FIG. 6 is a fragmentary sectional view of an end cap situated onthe flexible member;

[0017]FIG. 7 is a view similar to FIG. 6 showing a plurality of shearareas to enable the cap to separate from the flexible member when ashear stress exceeds a predetermined amount;

[0018]FIG. 8A is a sectional view taken along the line 8A-8A in FIG. 6;

[0019]FIG. 8B is a sectional view similar to FIG. 8A showing a flexiblemember with rounded corners;

[0020]FIG. 9 is graphical representation of a relationship between acompressive load for the flexible member relative to the length of themember as it shortens and flexes when the compression load exceeds apredetermined amount;

[0021]FIG. 10 is an illustration of another flexible member inaccordance with another embodiment of the invention;

[0022]FIG. 11 is a illustration of the flexible member shown in FIG. 10showing a shortened length L4;

[0023]FIG. 12 is a sectional view taken along the line 12-12 in FIG. 10;

[0024]FIG. 13 is a sectional view taken along the line 13-13 in FIG. 11;

[0025]FIG. 14 is a detailed drawing of a flexible arm;

[0026]FIGS. 15A and 15B are drawings of first and second endsrespectively of a flexible arm;

[0027]FIG. 16 is a drawing of a flexible arm looking in the direction16-16 of FIG. 14;

[0028]FIG. 17 is a side view of a composite link socket attachment;

[0029]FIG. 18 is a plan view of a composite link socket attachment;

[0030]FIG. 19 is a perspective view of another embodiment of theinvention;

[0031] FIGS. 20A and FIG. 20B illustrate another embodiment of theinvention;

[0032]FIGS. 21A and 21B illustrate load characteristics of theinvention,

[0033]FIG. 22 is a view illustrating another test;

[0034]FIG. 23 is a graph illustrating various features of the invention;and

[0035]FIG. 24 is another graph illustrating further load characteristicsof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Referring now to FIGS. 1 and 2A-2D, a windshield wiper system 10is shown comprising a first wiper 12 and a second wiper 14 for wiping awindshield 16. The wiper 12 comprises a wiper arm 12 a and blade 12 b,and wiper 14 comprises a wiper arm 14 a and blade 14 b.

[0037] The wiper system 10 further comprises a windshield wiper drivelinkage or linking means 18 comprising a first link arm 18 on which adrive motor 20 is fastened thereto by conventional means, such as aweld, nut and bolt, or the like. Notice that the frame link 18 comprisesa first pivot housing 21 and a second pivot housing 22 which is securedthereto. The housings 21 and 22 comprise a first rotatable pivot housingshaft 21 a and a second rotatable pivot housing shaft 22 a which aredrivingly coupled to wiper arms 12 a and 14 a (shown in phantom in FIG.1), respectively.

[0038] The first rotatable pivot housing shafts 21 a is coupled to afirst end 24 a of a drive plate 24. Likewise, the pivot housing shaft 22a is secured to a first end 26 a of a second drive plate 26, as bestillustrated in FIG. 1. An operating or “slave” link 23 couples a secondend 24 b of first drive plate 24 to a second end 26 b of second driveplate 26 such that the drive plates 24 and 26 operate synchronously torotatably drive the pivot housing shafts 21 a and 22 a in the directionof arrow A, thereby driving the wiper blades 12 b and 14 b.

[0039] The linkage or linking means 18 further comprises a motor drivelink or flexible arm 28 having a first end 28 a coupled to the secondend 24 b of the drive plate 24. The motor drive link or flexible arm 28further comprises a second end 28 b which is coupled to an output shaft20 a of motor 20 via a crank arm 30. In this regard, the crank arm 30comprises a crank arm ball (not shown) and the drive plate 24 comprisesa drive plate ball (not shown).

[0040] The arm 28 comprises an elongated rectangular member 29 (FIGS.3-5) comprising a socket 32 and socket 34 which are over-molded thereon.As best illustrated in FIGS. 3-6, the first end 28 a of motor drive linkor flexible arm 28 comprises the socket 32 for mounting onto the driveplate ball (not shown) on drive plates 24, and second end 28 b of motordrive link or flexible arm 28 comprises the socket 34 for receivingcrank arm ball (not shown) on crank arm 30. As best illustrated in FIGS.3-7, the first and second ends 28 a and 28 b comprise the sockets 32 and34, respectively. Notice that socket 32 (FIG. 6) defines a socket area40, respectively. It has been found that it is desirable to align thecenterline CL (FIG. 5) with the axis of shafts 20 a, 22 a and 24 a whenthe wipers 12 and 14 are in the park position.

[0041] As best illustrated in FIGS. 2A-2C and 3, flexible arm 28 definesa length L1, which in the embodiment being described is in excess of 250mm. During a fatigue condition, when the compressive load applied to thearm 28 exceeds a predetermined load (such as at least 30 percent of amaximum working load of flexible member 28 as defined below), theflexible arm 28 begins to flex or bend. This causes the flexible arm 28to shorten to a length L2, illustrated in FIG. 2D, and this length L2 isshorter than length L1. As illustrated in the graphs shown in FIG. 9which are referred to and described later herein, the compressive loadremains substantially constant as the flexible arm 28 continues to bendor flex and shorten for at least 5 mm after the compressive loadachieves the predetermined load.

[0042] As illustrated in FIGS. 3-5, the flexible arm 28 is preferablymade from a composite material of the type described later hereinrelative to Table 1. As best illustrated in FIG. 8A, the flexible arm 28is generally rectangular in cross-section and is generally elongated(FIGS. 3-5). It should be appreciated that the member 28 could beelliptical, circular or of some other geometry as desired. In theembodiment being described, the length L1 (FIGS. 2A and 3) of flexiblearm 28 is on the order of at least 250 mm, but it could be any suitablelength depending on the application.

[0043]FIG. 7 illustrates another embodiment of the invention where theflexible member 28 may be provided with sockets 32 and 34 with shearrelief areas 50 and 52 which enable the end caps 32 and 34 to shear awayor separate from member 29 when a predetermined stress is applied to theflexible member 28. Preferably, the predetermined stress is selected tobe just slightly below a break point or maximum load of the member 29 sothat, when the member 29 is about to reach its break point, one or moreof the sockets 32 or 34 are permitted to shear and separate themselvesfrom member 29 to avoid breakage. As illustrated in FIG. 7, line Cdefines a shear plane A_(s)=LW and a minimal cross section AC=HW, asshown by line D in FIG. 7. The shear stress along shear plane should notexceed the shearing strength which is defined as follows:

T=P/A _(s) =P/LW≦T _(y)

[0044] where:

[0045] A_(s)=LW

[0046] L=a length of shear plane (line C);

[0047] W=a width of member 28;

[0048] P=tensile load on member 28 as measured experimentally;

[0049] T=shear stress of member 28; and

[0050] T_(y)=yield shear stress of member 28.

[0051] A tensile stress on the minimum cross section should not exceed ayield stress as follows:

S=P/A _(c) =P/HW≦S _(y)

[0052] Where:

[0053] S=a tensile stress of member 28;

[0054] S_(y)=a yield stress of member 28;

[0055] P=a tensile load on member 28 as measured experimentally;

[0056] H=a height of member 28; and

[0057] W=a width of member 28.

[0058] The general operation of the linkage 18 will now be describedrelative to FIGS. 1 and 2A-2D. When a user actuates a wiper switch (notshown) the drive motor 20 is energized to cause the wipers to move froma park position (PP) through an inwipe position (IWP) towards an outwipeposition (OWP), back to the inwipe position and so on. When the userturns the switch to an off position (not shown), the drive motor 20drives the crank arm 30 to drive the motor drive link or flexible arm 28to attempt to drive wipers 12 and 14 from the inwipe position to thepark position. The motor 20 rotatably drives crank arm 30 which, inturn, drives the motor drive link or flexible arm 28 to drive the secondend 24 b of drive plate 24 in the direction of arrow B in FIG. 1. Theoperating link 23 responds by directly driving second end 26 b of driveplate 26. The movement of drive plates 24 and 26, in turn, rotatablydrive the pivot housing shafts 21 a and 22 a, respectively, to drive thefirst and second wipers 12 and 14 across the face of windshield 16 inresponse to rotation of the motor drive shaft 20 a.

[0059] As best illustrated in the FIGS. 2C and 2D, an excessive loadcondition may occur when snow, ice or some other material or condition(illustrated as 49 in FIGS. 2C and 2D) prevents the wiper blades frommoving, for example, from the inwipe position to the park position.However, the motor 20 continues to drive the motor drive link orflexible arm 28. Consequently, a compressive force or load is applied tothe arm 28. The flexible arm 28 bends or flexes to facilitate preventingdamage to the various components in the wiper system 10 when the loadapplied to the flexible arm 28 exceeds a predetermined load describedlater herein. Thus, it should be appreciated, that the flexible arm 28flexes to accommodate the compressive force or load mentioned earlierwhen the compressive force or load exceeds the predetermined load.

[0060] In the embodiment being described, it was determined empiricallythat, when the predetermined load was established is at least 130percent or more of a maximum normal running load, the arm 28 remainedrigid enough to handle the normal wiping, yet flexible enough to bendduring fatigue conditions. Thus, when the predetermined load exceedsabout 130 percent of the maximum normal running load for the flexiblearm 28, the wiper system 10 was able to operate with maximum efficiency,while protecting the components of the system 10. In the embodimentdescribed, the predetermined load is defined as follows:

P_(CR)=KE=1.3 P_(link)

[0061] where:

P_(CR)=the predetermined load;

P_(LINK)=a maximum normal running load for a comparably-sized steel orrigid link which does not flex;

[0062] K is a coefficient given by the relation:

K=π ² I÷L ²

[0063] E is the flexural modulus (MPa);

[0064] I is a moment of inertia in mm⁴; and

[0065] L is a length (mm) of flexible arm 28.

[0066] If the cross-sectional shape of member 28 is rounded on its edgesas shown in FIG. 8B, then the formula for the area moment of inertia (I)is calculated using the following equation:$I = {{\frac{1}{12}{W\left( {h - {2r}} \right)}^{3}} + {\frac{1}{6}\left( {b - {2r}} \right)} + {\frac{1}{2}{r\left( {h - r} \right)}^{2}\left( {b - {2r}} \right)} + {\frac{1}{4}\left\lbrack {r + \left( {h - {2r}} \right)^{2}} \right\rbrack}}$

[0067] where W, H and R are width, height and fillet radius,respectively, of the cross-section of member 28 shown in FIG. 8B.

[0068] Eight samples of composite material with dimensions as shown inTable 1 below were made and tested using an Instron testing machine. Theload and displacement were recorded and the testing results are shown inTable 1 and in the graph illustrated in FIG. 9.

[0069] As illustrated in Table I, the four different composite materialsincluded a molded glass laminate provided by Red Seal Electric Companyof Cleveland, Ohio; a molded epoxy resin provided by International Paperof Hampton, S.C.; a protruded polyester with oriented glass fibersprovided by National Composite Center of Dayton, Ohio; and a protrudedpolyester with unidirectional glass fibers provided by Polygon Companyof Walkerton, Ind.

[0070] It should be apparent from the Table I that the actual loads(P_(cnt-Exp).) compared vary favorably to theoretical loads(P_(cnt-Theory)). TABLE I Pcrit- L1 (mm) b (mm) h (mm) Pcrit- TheoryMaterial (Fig. 3) (Fig. 4) (Fig. 8) Exp. (N) (N) 1. Glastic Laminate 1a.253 12.7 3.3 61.71 68.74 1b. 253 19.09 3.3 94.96 103.33 1c. 253 25.323.3 131.91 137.05 2. Epoxy Resin (IP) 2a. 253 12.7 3.18 106.23 97.69 2b.253 19.09 3.18 206.52 146.85 2c. 253 25.32 3.18 290.02 238.47 3.Polyester 300 20 3.4 190.02 238.47 (NCC) 4. Fiberglass 305 31.7 2.42237.98 219.10

[0071]FIG. 9 graphically illustrates the Instron testing machineresults. Notice that, as the load on compressive arm 18 increased to inexcess of 300 Newton, the flexible arm 18 began to bend or flex (asshown in FIG. 2D), thereby causing the load to be distributed across theflexible member 28. Notice that the load remains substantially constanteven while the motor 20 (FIG. 1) continues to apply torque to theflexible arm 28.

[0072] FIGS. 10-13 illustrate another embodiment of the invention withlike parts being identified with the same part numbers, except that a“prime” mark (“′”) has been added thereto. In this embodiment, theflexible arm 28′ has a generally circular cross-section (as shown inFIG. 13) and comprises a plurality of areas of flex 62′ at areas wherethe flexible member 28′ defines an oval shape in cross section, as shownin FIG. 12. The points of weakness permit the flexible member 28′ toflex at the areas 62′ when the compressive load exceeds thepredetermined load, such as 30 percent higher than a maximum workingload of the flexible member 28′. Notice that the flexible member 28′defines a length L3 (FIG. 10) which is greater than the length L4 shownin FIG. 11. It has been found that the difference between the length L3and length L4, as well as the difference between length L1 and length L2referred to in the embodiment described above, is directly proportionalto the arcuate distance the drive motor 20 continues to drive the driveplate 24 (FIG. 1).

[0073] An ideal flexible member 28 would be perfectly rigid up to apredetermined load and perfectly elastic thereafter. Such a flexiblemember would have the stiffness necessary in excellent wipe patterncontrol, while yet limiting the peak loading of the system by elasticbuckling at a predetermined yield load. It has been found that acomposite link constructed as hereinafter described, provides a flexiblemember 28 which practically achieves such an operation. Post-bucklingbehavior of such a flexible member has been found to be very nearlyrigid/perfectly plastic in nature. Preferably, flexible member 28 ispultruded from a composite material offering tremendous strain atfracture, allowing the member to undergo appreciable axial compression.For comparison purposes, the composite material is capable of 2.6%strain at fracture whereas 7000 series aluminum is 0.7% at yield, 1080spring steel is 0.3% at yield, and 1009 CQ steel is 0.1% at yield.

[0074] When wiper system encounters a restriction in the wipe pattern,as illustrated in FIG. 2C , tremendous loads are generated. A compositelink provides a solution to this problem. After the restriction has beenencountered and the system loading has achieved a prescribed level, thecomposite link will buckle and become extremely compliant. FIG. 2Ddepicts this situation. Once the crank arm sweeps through the portion ofthe pattern that is restricted and the load diminishes, the compositelink will unload and revert back to the unbuckled shape. The compositelink has the added benefit of mass reduction since a composite link hasonly about 25% of the weight of its steel counterpart.

[0075] One of the problems in manufacturing a composite link assembly 28arises in the attachment of sockets 32, 34. Testing results have shownthat there is very little bonding strength if the sockets are directlyovermolded onto smooth composite links. Therefore, the ends of thecomposite link bars have to be treated to provide enough bondingstrength with the sockets and to avoid damaging the integrity of theresin-fiberglass structure. The following processes have beeninvestigated:

[0076] A. Mechanical Interlock

[0077] grooves top-bottom

[0078] grooves side-side vertical

[0079] grooves side-side horizontal

[0080] grooves side-side at neutral axis

[0081] Description of the Process

[0082] Machining of the cross grooves and the edge grooves requiresbasically the same machine. The only difference is in the size of thefixture system. The preferred grooving machine is a dedicated millingmachine with multiple diamond saws. The parts are loaded on a feedingsystem that holds the parts laying close to each other guides them underthe multiple fixed saws. Since the saws are under and above the parts,both ends and both sides are done at the same time. The cycle time ofthis process is quite short because the process is running continuouslyand one operator can take care of several machines. This system caneasily be used also to cut the parts at the length with the tolerancedesired. For the machining of the axial grooves, the saws have to movewith a vertical motion (down and back up) and the feeding system has tobe indexed. This system is much more complicated than the one firstdescribed above one, and the cycle time is longer, because the system isnot really continuous. Both sides and both ends can also be done at thesame time with this configuration. This system can be used to cut atlength the pultruded parts with the required accuracy.

[0083] B. Abrasive Processing

[0084] grooves top-bottom

[0085] grooves side-side vertical

[0086] grooves side-side horizontal

[0087] grooves side-side at neutral axis

[0088] Description of the Process:

[0089] This is a grit blasting process wherein a small gun creates astream of pressurized air for blasting an abrasive powder against a worksurface. It requires an exhaust system for removal of the dust. Theabrasive powder used for this application is aluminum oxide. The gritblast facility uses a feeding system (conveyor) for feeding the partsinto the grit blasting machine. The links (single file) are fed pastfour pressure guns to perform the specific notch cutting operation. Bothsides and both ends are done at the same time thanks to the four guns.

[0090] Process Parameters:

[0091] Airpressure: 50 PSI

[0092] Air consumption: 200 SCFM

[0093] Material Specification

[0094] Abrasive: aluminum oxide powder is recycled and runs in a closedloop, only 2% of the powder is lost during each shot.

[0095] Characteristics of the process—Flexible, but noisy. Tools wearrapidly and make lot of dust.

[0096] C-Laser Processing

[0097] grooves top-bottom

[0098] grooves side-side vertical

[0099] grooves side-side horizontal

[0100] grooves side-side at neutral axis

[0101] Roughens the link surface by burning the resin and exposing glassfiber

[0102] Description of the Process:

[0103] The system used to burn or cut the grooves in the composite linkis a laser marking system. The laser is an EO Q-switched Nd: YAGoperating in the second harmonic (532 nm). This kind of laser producespulses approximately 15 ns wide and combines both thermal and ablativeproperties. The process is accomplished by putting the composite linkbeneath the beam of a laser that has been defocussed to reduce the powerdensity. Nitrogen gas is blown just on the surface of the link to clearthe debris. Only one side and both ends of the link can be done at thesame time so the link has to be turned around by an operator. The linksare put on a conveyor (feeding system) that is indexed after each cycleof the laser so that two ends of two links are in the action window ofthe laser. The system has also a cooling station and an exhaust systemfor the fumes.

[0104] Process Parameters:

[0105] Nitrogen pressure: 30 PSI

[0106] Vertical position precision needed: ±{fraction (1/1000)} inch—

[0107] Frequency: 0 to 50 Hz

[0108] Material Specification:

[0109] Cleaning gas: nitrogen, argon but not air (could burn)

[0110] Crystal: Nd YAG

[0111] Characteristics of the Process

[0112] No noise

[0113] No wear of the tools

[0114] Very flexible but gas must be handled: argon or nitrogen

[0115] D-Plasma

[0116] Description of the Process:

[0117] The plasma burning station is composed of a power supply (samekind as the one for the plasma welding), two plasma torches and twomotion systems. The two torches (one above and one under the compositelinks) are moved close to the still link by the motion systemscontrolled by a control station. The composite links are still and theoperator puts them in the machine per batch. The plasma beam is anon-transferred beam (because the composite is not conductive) and iscreated by the electric power and argon gas that also protects theelectrodes from oxidation. The beam is 1 inch above the surface of thecomposite so that it doesn't touch the link but creates such a hightemperature that the resin of the composite burns but not the fibers.The system has also an exhaust system for the fumes and at least oneoperator for three plasma machines. The process has no noise and no wearon tools and is very flexible, but cannot be used to do grooves. Thisapproach requires the use and handling of argon gas.

[0118] Extreme caution should be used if the width, depth, spacing ornumber of grooves is changed or if the thickness of the pultruded rod isreduced below about 5.20 mm. When the member is buckled, the compositehas a tendency to delaminate, a phenomenon which manifests itself by theappearance of small cracks at the roots of the grooves. Extensivedevelopment testing was completed in order to find a grooveconfiguration that would meet the strength requirement when the link wasin tension, yet not be subject to delamination at peak mid-span stresslevels up to 690 MPa (100 ksi) that can occur when the composite link 28is buckled. FIGS. 14, 15A, 15B and 16, particularly reference numeral104 of FIG. 15A, illustrate the recommended top and bottom groovegeometry. Note the two sets of grooves 104 a and 104 b (FIG. 15A). Notethat the grooves 104 extend across the entire length W (FIG. 8B), butthey could extend only part way across the width if desired. Also, theyare shown to be linear, but they could comprise another shape, such ascurved. FIGS. 17 and 18 show the side-by-side grooves 106 at the neutralaxis of the link-bending plane. This design can reduce the peak bendingstress where the glass fibers are removed, so that weakness isminimized. Finally, FIGS. 19, 20A and 20B show various alternativeembodiments of circular and elongated or elliptic openings 108, 110 and112, respectively, that may be used to provide the interlocking jointwhen one of the sockets 32 or 34 is overmolded thereon.

[0119] Special attention must be paid to the resin flow during thesocket overmolding process. It is important to ensure that the Nylonmaterial completely fill the grooves machined onto the composite rod.Table II presents a design of experiment (DOE) matrix comparingthirty-two configurations of the invention. A C D E

Grooves Sur

e Finish Socket Material Attachment Method Pultrusion Priming 1 smoothsmooth nylon Insert mold pultrusion w/o at-prime 2 smooth ground axialfiber exposure acetal Insert mold pultrusion w/ at-prime 3 smooth plasmaaxial fiber exposure nylon adhesive assy w/o surface primer pultrusionw/o at-prime 4 smooth laser axial fiber exposure acetal adhesive assy w/surface primer pultrusion w/ at-prime 5 machined axial grooves smoothnylon Insert mold pultrusion w/ at-prime 6 machined axial grooves groundaxial fiber exposure acetal Insert mold pultrusion w/o at-prime 7machined axial grooves plasma axial fiber exposure nylon adhesive assyw/ surface primer pultrusion w/ at-prime 8 machined axial grooves laseraxial fiber exposure acetal adhesive assy w/o surface primer pultrusionw/o at-prime 9 machined cross grooves smooth acetal adhesive assy w/osurface primer pultrusion w/ at-prime 10 machined cross grooves groundaxial fiber exposure nylon adhesive assy w/ surface primer pultrusionw/o at-prime 11 machined cross grooves plasma axial fiber exposureacetal Insert mold pultrusion w/ at-prime 12 machined cross grooveslaser axial fiber exposure nylon Insert mold pultrusion w/o at-prime 13machined edge grooves smooth acetal adhesive assy w/ surface primerpultrusion w/o at-prime 14 machined edge grooves ground axial fiberexposure nylon adhesive assy w/o surface primer pultrusion w/ at-prime15 machined edge grooves plasma axial fiber exposure acetal Insert moldpultrusion w/o at-prime 16 machined edge grooves laser axial fiberexposure nylon Insert mold pultrusion w/ at-prime 17 laser axial groovessmooth acetal Insert mold pultrusion w/ at-prime 18 laser axial groovesground axial fiber exposure nylon Insert mold pultrusion w/o at-prime 19laser axial grooves plasma axial fiber exposure acetal adhesive assy w/osurface primer pultrusion w/ at-prime 20 laser axial grooves laser axialfiber exposure nylon adhesive assy w/ surface primer pultrusion w/oat-prime 21 laser cross grooves smooth acetal Insert mold pultrusion w/oat-prime 22 laser cross grooves ground axial fiber exposure nylon Insertmold pultrusion w/ at-prime 23 laser cross grooves plasma axial fiberexposure acetal adhesive assy w/ surface primer pultrusion w/o at-prime24 laser cross grooves laser axial fiber exposure nylon adhesive assyw/o surface primer pultrusion w/ at-prime 25

blast cross grooves smooth nylon adhesive assy w/o surface primerpultrusion w/o at-prime 26

blast cross grooves ground axial fiber exposure acetal adhesive assy w/surface primer pultrusion w/ at-prime 27

blast cross grooves plasma axial fiber exposure nylon Insert moldpultrusion w/o at-prime 28

blast cross grooves laser axial fiber exposure acetal Insert moldpultrusion w/ at-prime 29 ground cross grooves smooth nylon adhesiveassy w/ surface primer pultrusion w/ at-prime 30 ground cross groovesground axial fiber exposure acetal adhesive assy w/o surface primerpultrusion w/o at-prime 31 ground cross grooves plasma axial fiberexposure nylon Insert mold pultrusion w/ at-prime 32 ground crossgrooves laser axial fiber exposure acetal Insert mold pultrusion w/oat-prime

[0120] It should be appreciated that although the grooves are shown asillustrated in the figures, other groove configurations or arrangementof the grooves could be provided without departing from the scope of theinvention. For example, it has been found that providing a differentnumber of grooves on one surface, such as grooves 104 b on surface 28A1in FIG. 15A and three grooves 104 on the opposite surface, such asgrooves 104 a on surface 28A2 in FIG. 15A, with the grooves 104 a and104 b being arranged in a staggered configuration relative to each otherhas been found to be the preferred configuration.

[0121] Table III represents further DOE relative to socket attachmentfor eighteen samples. Note that each sample had a predetermined surfacefinish (smooth, abrasive-fine, abrasive-coarse, chemically etched, laseretched); machine grooves (smooth, which means no grooves; top and bottomgrooves as shown in FIG. 15A; and side-by-side grooves, as illustratedin FIG. 17); socket material from which the link 28 was made; the methodby which the sockets 32 and 34 were mounted onto the ends 28A and 28B ofarm 28; and protrusions having varying degrees of modulus. In theembodiment being described, the low modulus was provided to be about 40percent glass filled, moderate modulus was about 50 percent glass filledand high modulus was provided to be about 60 percent glass filled in theembodiment being described. TABLE III DOE of Socket Attachment 1 & 2 3 45 6 A B D E F Surface finish Machined grooves Socket materialAttachment/adhesives Pultrusions 1 smooth smooth nylon insert mold/hotcuring low modulus 2 smooth top-bottom acetal #1 mech attach/chem curemoderate modulus 3 smooth side-side acetal #2 insert mold/no adhesivehigh modulus 4 abrasive-find smooth nylon mech attach/chem cure moderatemodulus 5 abrasive-fine top-bottom acetal #1 insert mold/no adhesivehigh modulus 6 abrasive-fine side-side acetal #2 insert mold/hot curinglow modulus 7 abrasive-coarse smooth acetal #1 insert mold/hot curinghigh modulus 8 abrasive-coarse top-bottom acetal #2 mech attach/chemcure low modulus 9 abrasive-coarse side-side nylon insert mold/noadhesive moderate modulus 10 chemical etch smooth acetal #2 insertmold/no adhesive moderate modulus 11 chemical etch top-bottom nyloninsert mold/hot cunng high modulus 12 chemical etch side-side acetal #1mech attach/chem cure low modulus 13 laser etch #1 smooth acetal #1insert mold/no adhesive low modulus 14 laser etch #1 top-bottom acetal#2 insert mold/hot curing moderate modulus 15 laser etch #1 side-sidenylon mech attach/chem cure high modulus 16 laser etch #2 smooth acetal#2 mech attach/chem cure high modulus 17 laser etch #2 top-bottom nyloninsert mold/no adhesive low modulus 18 laser etch #2 side-side acetal #1insert mold/hot curing moderate modulus

[0122] It should be appreciated that in the embodiment being described,the desired groove size, groove spacing and number of grooves isselected to provide a predetermined configuration that optimized theinterlock between the socket, such as socket 32 and the arm 28. Thefollowing Table IV illustrates the various combinations of groove size,groove spacing and number of grooves selected. TABLE IV 1 2 3 A B CGroove Size Groove Spacing Number of Grooves 1 small #1 few 2 small #2moderate 3 small #3 many 4 medium #4 moderate 5 medium #5 many 6 medium#6 few 7 large #7 many 8 large #8 few 9 large #9 moderate

[0123] In the embodiment being described it was determined that thesample number 2 in Table III was preferred. This design was furthertested by conducted bearing strength tests (pulling through the ballsockets 32 and 34 using the fixture 116 in FIG. 21B); a joint strengthtest (using the fixture 110 illustrated in FIG. 21A); a static strength(bearing) test (Table VII); and a spectrum buckling durability test(Table VIII).

[0124] Two unique testing procedures were set up to test the strength ofthe interlock between the sockets 32 and 34 and the flexible arm 28.FIG. 21A illustrates a testing fixture 110 defining a U-shaped area 112for receiving a socket 32 and having a wall 110 a having a surface 110 a1 for engaging an end 32 a 1. It should be appreciated that the wall 110a comprises a slot 105 substantially corresponding to the dimension H(FIG. 8A) so that it can receive the arm 28. The arm 28 and fixture 110are moved in the direction of the arrows K and L until of the sockets 32and/or 34 separate, as illustrated in FIG. 21B. The results of the testsusing the sample 2 (Table III) is shown in the following Table V: TABLEV A. Bearing Strength Test (pull through ball sockets) Groove GrooveSample Max Load Size Spacing No. Pull Rate (N) Fail Mode (mm) (mm) 1 1.0 mm/mm 3100.7 upper - joint 0.5 2 2  1.0 mm/mm 2649.4 lower - socket0.5 2 3 10.0 mm/mm 2937.9 upper - socket 0.5 2 4 10.0 mm/mm 2946.6upper - joint 0.5 2 5 10.0 mm/mm 2871.6 lower - joint 0.5 2

[0125] TABLE VI B. Joint Strength Test (using stripping fixture) FailMode Groove Groove Max Joint Size Spacing Sample No. Pull rate Load (N)Joint (mm) (mm) 6 10.0 mm/min 3940.4 upper 0.5 2 7 10.0 mm/min 3902.9lower 0.5 2 8 10.0 mm/min 3724.3 lower 0.5 2 9 10.0 mm/min 3878.4 lower0.5 2 10 10.0 mm/min 3937.4 lower 0.5 2

[0126] A second bearing strength test was conducted to test the strengthof the socket 32 and length 28 and the joints therebetween. In thistest, a fixture 116 (FIG. 22) having a ball 118 was provided andinserted into the socket 32 as illustrated in FIG. 22. Loads were thenapplied in the directions of arrows M and N until the socket wall 32 a 2illustrate the results from the tests conducted. These results for thesame sample shown in Table VI.

[0127] In Table VII, the arm 28 was subject to a static strength test atthe loads indicated. Table VII illustrates the shear at the edge 32A1(FIG. 21A) and the arm 28. For example, note in one test shear did notoccur until an elongation of about 3 millimeters, which occurred in onetest after applying a maximum load of about 3170 Newtons. TABLE VII CWLStatic Strength (Bearing) Test Results Max Elongation Groove Load (N)(mm) Failure Mode Size (mm) Spacing (mm) 3227 3.14 Interface 1.0 3.003185 2.99 Interface 1.0 3.00 3170 3.00 Interface 1.0 3.00 3097 2.72Interface 1.0 3.00 3832 4.27 Interface 0.50 2.00 3787 3.74 Interface0.50 2.00 3246 3.08 Interface 0.50 2.00 3149 3.07 Interface 0.50 2.003187 3.11 Interface 0.50 2.00 3323 3.41 Interface 0.50 2.00 3225 3.22Interface 0.50 2.00 3379 3.33 Interface 0.50 2.00 3379 3.37 Interface0.50 2.00 3351 3.34 Interface 0.50 2.00

[0128] Interface: failure mode is shear at the socket-link jointinterface

[0129] Likewise, the following Table VIII illustrates further featuresof the invention showing various buckling durability tests over arepeated number of cycles and a corresponding failure mode which variedbased upon the groove configuration selected. For example, variousgroove configurations (e.g., 4/3, 4/4, etc.), such as a staggered fouron top, three on bottom configuration, were tested at various stresslevels as the sockets 32 and 34 were repeatedly brought towards eachother. The failure mode experienced resulted in either a delaminationwhere outside layers of the composite material separated or where bothdelamination or breaking of the arm 28 occurred. Sometimes at themidspan area (i.e., towards the middle of the arm 28 between its ends28A and 28B where maximum bending stress occurred. TABLE VIII CWLSpecimen Bucking Durability Tests ′Failure modes: Test Test GrooveGroove Groove Stress Displ Failure Size Spacing Configuration (ksi) (in)Cycles Mode r(mm) (mm) 4/3 90 0.669 29,457 Delam 1.00 4.00 4/3 80 0.53955,000 Both 1.00 4.00 4/3 70 0.422 240,000 Midspan 1.00 4.00 5/4 900.669 20,000 Delam 0.50 2.00 5/4 80 0.539 40,722 Both 0.50 2.00 5/4 700.422 291,902 Both 0.50 2.00 5/4 80 0.539 40,000 Delam 0.50 2.00 None100 0.812 15,000 Midspan None 90 0.669 25,000 Midspan None 80 0.539100,000 Midspan 0.50 3.00 4/4 90 0.669 25,000 Midspan 0.50 3.00 4/4 950.739 30,000 Midspan 0.50 3.00 4/4 100 0.812 15,000 Midspan 0.50 3.004/4 85 0.603 30,000 Midspan 0.50 3.00 4/4 80 0.539 60,000 Midspan 0.503.00 4/4 75 0.479 160,000 Midspan 0.50 3.00 4/4 70 0.422 210,000 Midspan0.50 3.00 4/4 95 0.739 25,000 Midspan 0.50 3.00 4/4 85 0.603 25,000Midspan 0.50 3.00

[0130] The results in Tables V through VIII illustrate the strength anddurability of the interlocking joint provided by the groove designbetween the sockets 32 and 34 and the arm 28 to which they are overmolded. Moreover, the sockets 32 and 34 resisted separation from theends of the arm 28 both in a static, non bending state as well as in abuckling or bent state during which a fatigued condition on thewindshield would normally be occurring.

[0131] While the method herein described, and the forms of apparatus forcarrying these methods into effect, constitute preferred embodiments ofthis invention, it is to be understood that the invention is not limitedto these precise methods and forms of apparatus, and that changes may bemade in either without departing from the scope of the invention, whichis defined in the appended claims.

What is claimed is:
 1. A windshield wiper drive linkage for use in awiper system comprising: a plurality of linkage arms; at least one ofsaid plurality of linkage arms comprising a composite flexible arm whichbends to facilitate preventing damage to components in said wiper systemwhen a compressive load applied to said at least one of said pluralityof linkage arms exceeds a predetermined load as a result of a fatiguecondition; said at least one of said plurality of linkage armscomprising comprise an interior groove on each side of an end of saidarm to facilitate providing an interlocking joint when a connector isovermolded onto each end.
 2. The windshield wiper drive linkage asrecited in claim 1 wherein said flexible arm comprises a modulus ofelasticity of at least 50,000 psi.
 3. The windshield wiper drive linkageas recited in claim 1 wherein said predetermined load is approximately30 percent higher than a highest working load.
 4. The windshield wiperdrive linkage as recited in claim 1 wherein said predetermined load isapproximately 300 Newton or higher.
 5. The windshield wiper drivelinkage as recited in claim 1 wherein said flexible arm comprises apultruded composite comprising 40-60 percent (in weight) glass fibers.6. The windshield wiper drive linkage as recited in claim 3 wherein saidflexible arm comprises a length of approximately 250 mm or more.
 7. Thewindshield wiper drive linkage as recited in claim 1 wherein saidflexible arm is rectangular in cross section.
 8. The windshield wiperdrive linkage as recited in claim 1 wherein said a flexible armcomprises a first end coupled to a drive arm and a second end coupled toa driven arm; said first end and said second end defining a firstdistance when said compressive load is less than said predetermined loadand defining a second distance when said compressive load exceeds saidpredetermined load, wherein said second distance is less than said firstdistance.
 9. The windshield wiper drive linkage as recited in claim 1wherein said compressive load remains substantially constant as saidflexible arm shortens at least 25 mm after said compressive load exceedssaid predetermined load.
 10. The windshield wiper drive linkage asrecited in claim 9 wherein said flexible arm is a fiber-reinforcedcomposite or thermoset carrier.
 11. The windshield wiper drive linkageas recited in claim 1 wherein said interior groove defines a crescentshape.
 12. The windshield wiper drive linkage as recited in claim 1wherein said interior groove extends substantially parallel to an axisof said arm.
 13. The windshield wiper drive linkage as recited in claim1 wherein said connector comprises a ball socket.
 14. A wiper systemcomprising: a first wiper; a second wiper; a windshield wiper drivelinkage coupled to said first and second wipers; a drive motor coupledto said windshield wiper drive linkage; and said windshield wiper drivelinkage comprising: a plurality of linkage arms coupled to said firstand second wipers and said drive motor; at least one of said pluralityof linkage arms comprising a composite flexible arm which bends tofacilitate preventing damage to components in said wiper system when acompressive load applied to said at least one of said plurality oflinkage arms exceeds a predetermined load as a result of a fatiguecondition; said at least one of said plurality of linkage armscomprising an interior groove on each side of an end of said arm tofacilitate providing an interlocking joint when a connector isovermolded onto each end.
 15. The windshield wiper drive linkage asrecited in claim 14 wherein said flexible arm comprises a modulus ofelasticity of at least 50,000 psi.
 16. The windshield wiper drivelinkage as recited in claim 14 wherein said predetermined load isapproximately 30 percent higher than a highest working load.
 17. Thewindshield wiper drive linkage as recited in claim 14 wherein saidpredetermined load is approximately 300 Newton or higher.
 18. Thewindshield wiper drive linkage as recited in claim 14 wherein saidflexible arm comprises a pultruded composite comprising 40-60 percent(in weight) glass fibers.
 19. The windshield wiper drive linkage asrecited in claim 16 wherein said flexible arm comprises a length ofapproximately 250 mm or more.
 20. The windshield wiper drive linkage asrecited in claim 14 wherein said flexible arm is rectangular in crosssection.
 21. The windshield wiper drive linkage as recited in claim 14wherein said a flexible arm comprises a first end coupled to a drive armand a second end coupled to a driven arm; said first end and said secondend defining a first distance when said compressive load is less thansaid predetermined load and defining a second distance when saidcompressive load exceeds said predetermined load, wherein said seconddistance is less than said first distance.
 22. The windshield wiperdrive linkage as recited in claim 14 wherein said compressive loadremains substantially constant as said flexible arm shortens at least 25mm after said compressive load exceeds said predetermined load.
 23. Thewindshield wiper drive linkage as recited in claim 14 wherein saidflexible arm is a fiber-reinforced composite or thermoset carrier. 24.The windshield wiper drive linkage as recited in claim 14 wherein saidinterior groove defines a crescent shape.
 25. The windshield wiper drivelinkage as recited in claim 24 wherein said interior groove extendssubstantially parallel to an axis of said arm.
 26. The windshield wiperdrive linkage as recited in claim 14 wherein said connector comprises aball socket.